Phenyl and fluorenyl substituted phenyl-pyrazole complexes of Ir

ABSTRACT

The invention provides emissive materials and organic light emitting devices using the emissive materials in an emissive layer disposed between and electrically connected to an anode and a cathode. The emissive materials include compounds with the following structure: 
                         
wherein at least one of R 8  to R 14  is phenyl or substituted phenyl, and/or at least two of R 8  to R 14  that are adjacent are part of a fluorenyl group. The emissive materials have enhanced electroluminescent efficiency and improved lifetime when incorporated into light emitting devices.

RELATED APPLICATIONS

This application is a division of U.S. patent application Ser. No.12/069,610, filed Feb. 11, 2008, now U.S. Pat. No. 8,043,724, which is adivision of U.S. patent application Ser. No. 10/807,738, filed Mar. 24,2004, now U.S. Pat. No. 7,338,722, which is related to and claimspriority from U.S. Provisional Patent Application 60/457,012, filed Mar.24, 2003, the disclosures of which are incorporated by reference hereinin their entirety.

RESEARCH AGREEMENTS

The claimed invention was made by, on behalf of, and/or in connectionwith one or more of the following parties to a joint universitycorporation research agreement: Princeton University, The University ofSouthern California, The Regents of the University of Michigan, andUniversal Display Corporation. The agreement was in effect on and beforethe date the claimed invention was made, and the claimed invention wasmade as a result of activities undertaken within the scope of theagreement.

FIELD OF THE INVENTION

The present invention relates to organic light emitting devices (OLEDs),and more specifically to phosphorescent organic materials used in suchdevices. More specifically, the present invention relates tophosphorescent materials with improved electroluminescent efficiencieswhen incorporated into an OLED.

BACKGROUND

Optoelectronic devices that make use of organic materials are becomingincreasingly desirable for a number of reasons. Many of the materialsused to make such devices are relatively inexpensive, so organicoptoelectronic devices have the potential for cost advantages overinorganic devices. In addition, the inherent properties of organicmaterials, such as their flexibility, may make them well suited forparticular applications such as fabrication on a flexible substrate.Examples of organic optoelectronic devices include organic lightemitting devices (OLEDs), organic phototransistors, organic photovoltaiccells, and organic photodetectors. For OLEDs, the organic materials mayhave performance advantages over conventional materials. For example,the wavelength at which an organic emissive layer emits light maygenerally be readily tuned with appropriate dopants.

As used herein, the term “organic” includes polymeric materials as wellas small molecule organic materials that may be used to fabricateorganic optoelectronic devices. “Small molecule” refers to any organicmaterial that is not a polymer, and “small molecules” may actually bequite large. Small molecules may include repeat units in somecircumstances. For example, using a long chain alkyl group as asubstituent does not remove a molecule from the “small molecule” class.Small molecules may also be incorporated into polymers, for example as apendent group on a polymer backbone or as a part of the backbone. Smallmolecules may also serve as the core moiety of a dendrimer, whichconsists of a series of chemical shells built on the core moiety. Thecore moiety of a dendrimer may be a fluorescent or phosphorescent smallmolecule emitter. A dendrimer may be a “small molecule,” and it isbelieved that all dendrimers currently used in the field of OLEDs aresmall molecules.

OLEDs make use of thin organic films that emit light when voltage isapplied across the device. OLEDs are becoming an increasinglyinteresting technology for use in applications such as flat paneldisplays, illumination, and backlighting. Several OLED materials andconfigurations are described in U.S. Pat. Nos. 5,844,363, 6,303,238, and5,707,745, which are incorporated herein by reference in their entirety.

OLED devices are generally (but not always) intended to emit lightthrough at least one of the electrodes, and one or more transparentelectrodes may be useful in organic optoelectronic devices. For example,a transparent electrode material, such as indium tin oxide (ITO), may beused as the bottom electrode. A transparent top electrode, such asdisclosed in U.S. Pat. Nos. 5,703,436 and 5,707,745, which areincorporated by reference in their entireties, may also be used. For adevice intended to emit light only through the bottom electrode, the topelectrode does not need to be transparent, and may be comprised of athick and reflective metal layer having a high electrical conductivity.Similarly, for a device intended to emit light only through the topelectrode, the bottom electrode may be opaque and/or reflective. Wherean electrode does not need to be transparent, using a thicker layer mayprovide better conductivity, and using a reflective electrode mayincrease the amount of light emitted through the other electrode, byreflecting light back towards the transparent electrode. Fullytransparent devices may also be fabricated, where both electrodes aretransparent. Side emitting OLEDs may also be fabricated, and one or bothelectrodes may be opaque or reflective in such devices.

As used herein, “top” means furthest away from the substrate, while“bottom” means closest to the substrate. For example, for a devicehaving two electrodes, the bottom electrode is the electrode closest tothe substrate, and is generally the first electrode fabricated. Thebottom electrode has two surfaces, a bottom surface closest to thesubstrate, and a top surface further away from the substrate. Where afirst layer is described as “disposed over” a second layer, the firstlayer is disposed further away from substrate. There may be other layersbetween the first and second layer, unless it is specified that thefirst layer is “in physical contact with” the second layer. For example,a cathode may be described as “disposed over” an anode, even thoughthere are various organic layers in between.

As used herein, “solution processible” means capable of being dissolved,dispersed, or transported in and/or deposited from a liquid medium,either in solution or suspension form.

One application for phosphorescent emissive molecules is a full colordisplay. Industry standards for such a display call for pixels adaptedto emit particular colors, referred to as “saturated” colors. Inparticular, these standards call for saturated red, green, and bluepixels. Color may be measured using CIE coordinates, which are wellknown to the art.

Industry standards call for the lifetime of such full color displays tobe at least about 5000 hours. In addition, high stability and efficiencyare important characteristics of high quality displays. Theserequirements have helped generate a need for phosphorescent emissivematerials that exhibit longer lifetimes, higher stability, and higherefficiency in the red, green and blue wavelength regimes than have beenachieved in the prior art.

One example of a green emissive molecule is tris(2-phenylpyridine)iridium, denoted Ir(ppy)₃, which has following structure:

In this, and later figures herein, we depict the dative bond fromnitrogen to metal (here, Ir) as a straight line. Ir(ppy)₃ emits aspectrum at CIE 0.30, 0.63, and has a half-life of about 10,000 hours atan initial luminance of 500 cd/m², and a quantum efficiency of about 6%.Kwong et al., Appl. Phys. Lett., 81, 162 (2002).

SUMMARY OF THE INVENTION

An organic light emitting device is provided. The device has an anode, acathode, and an emissive layer disposed between and electricallyconnected to the anode and the cathode. The emissive layer may furtherinclude a compound with the following structure:

wherein

-   -   M is a metal having an atomic weight greater than 40;    -   (C—N) is a substituted or unsubstituted cyclometallated ligand,        and (C—N) is different from at least one other ligand attached        to the metal;    -   each of R₈ to R₁₄ is independently selected from hydrogen,        alkyl, alkenyl, alkynyl, alkylaryl, CN, CF₃, NO₂, halo, aryl,        heteroaryl, substituted aryl, substituted heteroaryl, or a        heterocyclic group;    -   m may be 0, or have a value of at least 1;    -   n has a value of at least 1, where, when n is 3, none of R₈ to        R₁₄ is a cyano group;    -   m+n is the maximum number of ligands that may be attached to the        metal; and    -   optionally, any two adjacent substituted positions together        form, independently, a fused 4- to 7-member cyclic group,        wherein said cyclic group is cycloalkyl, cycloheteroalkyl, aryl,        or heteroaryl, and wherein the 4- to 7-member cyclic group may        be optionally substituted with substituent R. Preferably, at        least one of R₈ to R₁₄ is phenyl or substituted phenyl, and/or        at least two of R₈ to R₁₄ that are adjacent are part of a        fluorenyl group.

The emissive layer may further include a compound comprising a metalbonded to at least a first ligand and a second ligand, in which thefirst ligand has a triplet energy corresponding to a wavelength that isat least 80 nm greater than the wavelength corresponding to the tripletenergy of other ligands. The compound may have only one first ligandbound to the metal. Each ligand may be organometallic.

The emissive material may have enhanced electroluminescent efficiencyand improved lifetime when incorporated into a light emitting device.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an organic light emitting device having separate electrontransport, hole transport, and emissive layers, as well as other layers.

FIG. 2 shows an inverted organic light emitting device that does nothave a separate electron transport layer.

FIG. 3 shows the emission spectra at 77 K for fac-Ir(3bppz)₃,fac-Ir(4bppz)₃, fac-Ir(14dppz)₃, fac-Ir(4bpppz)₃, fac-Ir(2dmflpz)₃.

FIG. 4 shows the emission spectra at room temperature forfac-Ir(3bppz)₃, fac-Ir(4bppz)₃, fac-Ir(14dppz)₃, fac-Ir(4bpppz)₃,fac-Ir(2dmflpz)₃.

FIG. 5 shows the emission spectra for fac-Ir(14dppz)₃, fac-Ir(4bpppz)₃,fac-Ir(2dmflpz)₃ in polystyrene at room temperature.

DETAILED DESCRIPTION

Generally, an OLED comprises at least one organic layer disposed betweenand electrically connected to an anode and a cathode. As used herein,the term “disposed between and electrically connected to” does notindicate that the recited layers are necessarily adjacent and in directcontact. Rather, it allows for the disposition of additional layersbetween the recited layers. When a current is applied, the anode injectsholes and the cathode injects electrons into the organic layer(s). Theinjected holes and electrons each migrate toward the oppositely chargedelectrode. When an electron and hole localize on the same molecule, an“exciton,” which is a localized electron-hole pair having an excitedenergy state, is formed. Light is emitted when the exciton relaxes via aphotoemissive mechanism. In some cases, the exciton may be localized onan excimer or an exciplex. Non-radiative mechanisms, such as thermalrelaxation, may also occur, but are generally considered undesirable.

The initial OLEDs used emissive molecules that emitted light from theirsinglet states (“fluorescence”) as disclosed, for example, in U.S. Pat.No. 4,769,292, which is incorporated by reference in its entirety.Fluorescent emission generally occurs in a time frame of less than 10nanoseconds.

More recently, OLEDs having emissive materials that emit light fromtriplet states (“phosphorescence”) have been demonstrated. Baldo et al.,“Highly Efficient Phosphorescent Emission from OrganicElectroluminescent Devices,” Nature, vol. 395, 151-154, 1998;(“Baldo-I”) and Baldo et al., “Very high-efficiency green organiclight-emitting devices based on electrophosphorescence,” Appl. Phys.Lett., vol. 75, No. 3, 4-6 (1999) (“Baldo-II”), which are incorporatedby reference in their entireties. Phosphorescence may be referred to asa “forbidden” transition because the transition requires a change inspin states, and quantum mechanics indicates that such a transition isnot favored. As a result, phosphorescence generally occurs in a timeframe exceeding at least 10 nanoseconds, and typically greater than 100nanoseconds. If the natural radiative lifetime of phosphorescence is toolong, triplets may decay by a non-radiative mechanism, such that nolight is emitted. Organic phosphorescence is also often observed inmolecules containing heteroatoms with unshared pairs of electrons atvery low temperatures. 2,2′-bipyridine is such a molecule. Non-radiativedecay mechanisms are typically temperature dependent, such that amaterial that exhibits phosphorescence at liquid nitrogen temperaturesmay not exhibit phosphorescence at room temperature. However, asdemonstrated by Baldo, this problem may be addressed by selectingphosphorescent compounds that do phosphoresce at room temperature.Representative emissive layers include doped or un-doped phosphorescentorganometallic materials such as disclosed in U.S. Pat. Nos. 6,303,238and 6,310,360; U.S. Patent Application Publication Nos. 2002-0034656;2002-0182441; and 2003-0072964; and WO-02/074015.

Generally, the excitons in an OLED are believed to be created in a ratioof about 3:1, i.e., approximately 75% triplets and 25% singlets. See,Adachi et al., “Nearly 100% Internal Phosphorescent Efficiency In AnOrganic Light Emitting Device,” J. Appl. Phys., 90, 5048 (2001), whichis incorporated by reference in its entirety. In many cases, singletexcitons may readily transfer their energy to triplet excited states via“intersystem crossing,” whereas triplet excitons may not readilytransfer their energy to singlet excited states. As a result, 100%internal quantum efficiency is theoretically possible withphosphorescent OLEDs. In a fluorescent device, the energy of tripletexcitons is generally lost to radiationless decay processes that heat-upthe device, resulting in much lower internal quantum efficiencies. OLEDsutilizing phosphorescent materials that emit from triplet excited statesare disclosed, for example, in U.S. Pat. No. 6,303,238, which isincorporated by reference in its entirety.

Phosphorescence may be preceded by a transition from a triplet excitedstate to an intermediate non-triplet state from which the emissive decayoccurs. For example, organic molecules coordinated to lanthanideelements often phosphoresce from excited states localized on thelanthanide metal. However, such materials do not phosphoresce directlyfrom a triplet excited state but instead emit from an atomic excitedstate centered on the lanthanide metal ion. The europium diketonatecomplexes illustrate one group of these types of species.

Phosphorescence from triplets can be enhanced over fluorescence byconfining, preferably through bonding, the organic molecule in closeproximity to an atom of high atomic number. This phenomenon, called theheavy atom effect, is created by a mechanism known as spin-orbitcoupling. Such a phosphorescent transition may be observed from anexcited metal-to-ligand charge transfer (MLCT) state of anorganometallic molecule such as tris(2-phenylpyridine)iridium(III).

As used herein, the term “triplet energy” refers to an energycorresponding to the highest energy feature discernable in thephosphorescence spectrum of a given material. The highest energy featureis not necessarily the peak having the greatest intensity in thephosphorescence spectrum, and could, for example, be a local maximum ofa clear shoulder on the high energy side of such a peak.

FIG. 1 shows an organic light emitting device 100. The figures are notnecessarily drawn to scale. Device 100 may include a substrate 110, ananode 115, a hole injection layer 120, a hole transport layer 125, anelectron blocking layer 130, an emissive layer 135, a hole blockinglayer 140, an electron transport layer 145, an electron injection layer150, a protective layer 155, and a cathode 160. Cathode 160 is acompound cathode having a first conductive layer 162 and a secondconductive layer 164. Device 100 may be fabricated by depositing thelayers described, in order.

Substrate 110 may be any suitable substrate that provides desiredstructural properties. Substrate 110 may be flexible or rigid. Substrate110 may be transparent, translucent, or opaque. Plastic and glass areexamples of preferred rigid substrate materials. Plastic and metal foilsare examples of preferred flexible substrate materials. Substrate 110may be a semiconductor material in order to facilitate the fabricationof circuitry. For example, substrate 110 may be a silicon wafer uponwhich circuits are fabricated, capable of controlling OLEDs subsequentlydeposited on the substrate. Other substrates may be used. The materialand thickness of substrate 110 may be chosen to obtain desiredstructural and optical properties.

Anode 115 may be any suitable anode that is sufficiently conductive totransport holes to the organic layers. The material of anode 115preferably has a work function higher than about 4 eV (a “high workfunction material”). Preferred anode materials include conductive metaloxides, such as indium tin oxide (ITO) and indium zinc oxide (IZO),aluminum zinc oxide (AlZnO), and metals. Anode 115 (and substrate 110)may be sufficiently transparent to create a bottom-emitting device. Apreferred transparent substrate and anode combination is commerciallyavailable ITO (anode) deposited on glass or plastic (substrate). Aflexible and transparent substrate-anode combination is disclosed inU.S. Pat. No. 5,844,363, which is incorporated by reference in itsentirety. Anode 115 may be opaque and/or reflective. A reflective anode115 may be preferred for some top-emitting devices, to increase theamount of light emitted from the top of the device. The material andthickness of anode 115 may be chosen to obtain desired conductive andoptical properties. Where anode 115 is transparent, there may be a rangeof thickness for a particular material that is thick enough to providethe desired conductivity, yet thin enough to provide the desired degreeof transparency. Other anode materials and structures may be used.

Hole transport layer 125 may include a material capable of transportingholes. Hole transport layer 130 may be intrinsic (undoped), or doped.Doping may be used to enhance conductivity. α-NPD and TPD are examplesof intrinsic hole transport layers. An example of a p-doped holetransport layer is m-MTDATA doped with F₄-TCNQ at a molar ratio of 50:1,as disclosed in U.S. patent application Ser. No. 10/173,682 to Forrestet al. (published as Publication No. 2003/0230980), which isincorporated by reference in its entirety. Other hole transport layersmay be used.

Emissive layer 135 may include an organic material capable of emittinglight when a current is passed between anode 115 and cathode 160.Preferably, emissive layer 135 contains a phosphorescent emissivematerial, although fluorescent emissive materials may also be used.Phosphorescent materials are preferred because of the higher luminescentefficiencies associated with such materials. Emissive layer 135 may alsocomprise a host material capable of transporting electrons and/or holes,doped with an emissive material that may trap electrons, holes, and/orexcitons, such that excitons relax from the emissive material via aphotoemissive mechanism. Emissive layer 135 may comprise a singlematerial that combines transport and emissive properties. Whether theemissive material is a dopant or a major constituent, emissive layer 135may comprise other materials, such as dopants that tune the emission ofthe emissive material. Emissive layer 135 may include a plurality ofemissive materials capable of, in combination, emitting a desiredspectrum of light. Examples of phosphorescent emissive materials includeIr(ppy)₃. Examples of fluorescent emissive materials include DCM andDMQA. Examples of host materials include Alq₃, CBP, and mCP. Examples ofemissive and host materials are disclosed in U.S. Pat. No. 6,303,238 toThompson et al., which is incorporated by reference in its entirety.Emissive material may be included in emissive layer 135 in a number ofways. For example, an emissive small molecule may be incorporated into apolymer. Other emissive layer materials and structures may be used.

Electron transport layer 140 may include a material capable oftransporting electrons. Electron transport layer 140 may be intrinsic(undoped), or doped. Doping may be used to enhance conductivity. Alq₃ isan example of an intrinsic electron transport layer. An example of ann-doped electron transport layer is BPhen doped with Li at a molar ratioof 1:1, as disclosed in U.S. patent application Ser. No. 10/173,682 toForrest et al. (published as Publication No. 2003/0230980), which isincorporated by reference in its entirety. Other electron transportlayers may be used.

The charge carrying component of the electron transport layer may beselected such that electrons can be efficiently injected from thecathode into the LUMO (Lowest Unoccupied Molecular Orbital) level of theelectron transport layer. The “charge carrying component” is thematerial responsible for the LUMO that actually transports electrons.This component may be the base material, or it may be a dopant. The LUMOlevel of an organic material may be generally characterized by theelectron affinity of that material and the relative electron injectionefficiently of a cathode may be generally characterized in terms of thework function of the cathode material. This means that the preferredproperties of an electron transport layer and the adjacent cathode maybe specified in terms of the electron affinity of the charge carryingcomponent of the ETL and the work function of the cathode material. Inparticular, so as to achieve high electron injection efficiency, thework function of the cathode material is preferably not greater than theelectron affinity of the charge carrying component of the electrontransport layer by more than about 0.75 eV, more preferably, by not morethan about 0.5 eV. Similar considerations apply to any layer into whichelectrons are being injected.

Cathode 160 may be any suitable material or combination of materialsknown to the art, such that cathode 160 is capable of conductingelectrons and injecting them into the organic layers of device 100.Cathode 160 may be transparent or opaque, and may be reflective. Metalsand metal oxides are examples of suitable cathode materials. Cathode 160may be a single layer, or may have a compound structure. FIG. 1 shows acompound cathode 160 having a thin metal layer 162 and a thickerconductive metal oxide layer 164. In a compound cathode, preferredmaterials for the thicker layer 164 include ITO, IZO, and othermaterials known to the art. U.S. Pat. Nos. 5,703,436 and 5,707,745,which are incorporated by reference in their entireties, discloseexamples of cathodes including compound cathodes having a thin layer ofmetal such as Mg:Ag with an overlying transparent,electrically-conductive, sputter-deposited ITO layer. The part ofcathode 160 that is in contact with the underlying organic layer,whether it is a single layer cathode 160, the thin metal layer 162 of acompound cathode, or some other part, is preferably made of a materialhaving a work function lower than about 4 eV (a “low work functionmaterial”). Other cathode materials and structures may be used.

Blocking layers may be used to reduce the number of charge carriers(electrons or holes) and/or excitons that leave the emissive layer. Anelectron blocking layer 130 may be disposed between emissive layer 135and the hole transport layer 125, to block electrons from leavingemissive layer 135 in the direction of hole transport layer 125.Similarly, a hole blocking layer 140 may be disposed between emissivelayer 135 and electron transport layer 145, to block holes from leavingemissive layer 135 in the direction of electron transport layer 140.Blocking layers may also be used to block excitons from diffusing out ofthe emissive layer. The theory and use of blocking layers is describedin more detail in U.S. Pat. No. 6,097,147 and U.S. patent applicationSer. No. 10/173,682 to Forrest et al. (published as Publication No.2003/0230980), which are incorporated by reference in their entireties.

As used herein, the term “blocking layer” means that the layer providesa barrier that significantly inhibits transport of charge carriersand/or excitons through the device, without suggesting that the layernecessarily completely blocks the charge carriers and/or excitons. Thepresence of such a blocking layer in a device may result insubstantially higher efficiencies as compared to a similar devicelacking a blocking layer. In addition, a blocking layer may be used toconfine emission to a desired region of an OLED.

Generally, injection layers are comprised of a material that may improvethe injection of charge carriers from one layer, such as an electrode oran organic layer, into an adjacent organic layer. Injection layers mayalso perform a charge transport function. In device 100, hole injectionlayer 120 may be any layer that improves the injection of holes fromanode 115 into hole transport layer 125. CuPc is an example of amaterial that may be used as a hole injection layer from an ITO anode115, and other anodes. In device 100, electron injection layer 150 maybe any layer that improves the injection of electrons into electrontransport layer 145. LiF/Al is an example of a material that may be usedas an electron injection layer into an electron transport layer from anadjacent layer. Other materials or combinations of materials may be usedfor injection layers. Depending upon the configuration of a particulardevice, injection layers may be disposed at locations different thanthose shown in device 100. More examples of injection layers areprovided in U.S. patent application Ser. No. 09/931,948 to Lu et al.,now U.S. Pat. No. 7,071,615, which is incorporated by reference in itsentirety. A hole injection layer may comprise a solution depositedmaterial, such as a spin-coated polymer, e.g., PEDOT:PSS, or it may be avapor deposited small molecule material, e.g., CuPc or MTDATA.

A hole injection layer (HIL) may planarize or wet the anode surface soas to provide efficient hole injection from the anode into the holeinjecting material. A hole injection layer may also have a chargecarrying component having HOMO (Highest Occupied Molecular Orbital)energy levels that favorably match up, as defined by theirherein-described relative ionization potential (IP) energies, with theadjacent anode layer on one side of the HIL and the hole transportinglayer on the opposite side of the HIL. The “charge carrying component”is the material responsible for the HOMO that actually transports holes.This component may be the base material of the HIL, or it may be adopant. Using a doped HIL allows the dopant to be selected for itselectrical properties, and the host to be selected for morphologicalproperties such as wetting, flexibility, toughness, etc. Preferredproperties for the HIL material are such that holes can be efficientlyinjected from the anode into the HIL material. In particular, the chargecarrying component of the HIL preferably has an IP not more than about0.7 eV greater that the IP of the anode material. More preferably, thecharge carrying component has an IP not more than about 0.5 eV greaterthan the anode material. Similar considerations apply to any layer intowhich holes are being injected. HIL materials are further distinguishedfrom conventional hole transporting materials that are typically used inthe hole transporting layer of an OLED in that such HIL materials mayhave a hole conductivity that is substantially less than the holeconductivity of conventional hole transporting materials. The thicknessof the HIL of the present invention may be thick enough to helpplanarize or wet the surface of the anode layer. For example, an HILthickness of as little as 10 nm may be acceptable for a very smoothanode surface. However, since anode surfaces tend to be very rough, athickness for the HIL of up to 50 nm may be desired in some cases.

A protective layer may be used to protect underlying layers duringsubsequent fabrication processes. For example, the processes used tofabricate metal or metal oxide top electrodes may damage organic layers,and a protective layer may be used to reduce or eliminate such damage.In device 100, protective layer 155 may reduce damage to underlyingorganic layers during the fabrication of cathode 160. Preferably, aprotective layer has a high carrier mobility for the type of carrierthat it transports (electrons in device 100), such that it does notsignificantly increase the operating voltage of device 100. CuPc, BCP,and various metal phthalocyanines are examples of materials that may beused in protective layers. Other materials or combinations of materialsmay be used. The thickness of protective layer 155 is preferably thickenough that there is little or no damage to underlying layers due tofabrication processes that occur after organic protective layer 160 isdeposited, yet not so thick as to significantly increase the operatingvoltage of device 100. Protective layer 155 may be doped to increase itsconductivity. For example, a CuPc or BCP protective layer 160 may bedoped with Li. A more detailed description of protective layers may befound in U.S. patent application Ser. No. 09/931,948 to Lu et al., nowU.S. Pat. No. 7,071,615, which is incorporated by reference in itsentirety.

FIG. 2 shows an inverted OLED 200. The device includes a substrate 210,an cathode 215, an emissive layer 220, a hole transport layer 225, andan anode 230. Device 200 may be fabricated by depositing the layersdescribed, in order. Because the most common OLED configuration has acathode disposed over the anode, and device 200 has cathode 215 disposedunder anode 230, device 200 may be referred to as an “inverted” OLED.Materials similar to those described with respect to device 100 may beused in the corresponding layers of device 200. FIG. 2 provides oneexample of how some layers may be omitted from the structure of device100.

The simple layered structure illustrated in FIGS. 1 and 2 is provided byway of non-limiting example, and it is understood that embodiments ofthe invention may be used in connection with a wide variety of otherstructures. The specific materials and structures described areexemplary in nature, and other materials and structures may be used.Functional OLEDs may be achieved by combining the various layersdescribed in different ways, or layers may be omitted entirely, based ondesign, performance, and cost factors. Other layers not specificallydescribed may also be included. Materials other than those specificallydescribed may be used. Although many of the examples provided hereindescribe various layers as comprising a single material, it isunderstood that combinations of materials, such as a mixture of host anddopant, or more generally a mixture, may be used. In addition, thelayers may have various sublayers. The names given to the various layersherein are not intended to be strictly limiting. For example, in device200, hole transport layer 225 transports holes and injects holes intoemissive layer 220, and may be described as a hole transport layer or ahole injection layer. In one embodiment, an OLED may be described ashaving an “organic layer” disposed between a cathode and an anode. Thisorganic layer may comprise a single layer, or may further comprisemultiple layers of different organic materials as described, forexample, with respect to FIGS. 1 and 2.

Structures and materials not specifically described may also be used,such as OLEDs comprised of polymeric materials (PLEDs) such as disclosedin U.S. Pat. No. 5,247,190, Friend et al., which is incorporated byreference in its entirety. By way of further example, OLEDs having asingle organic layer may be used. OLEDs may be stacked, for example asdescribed in U.S. Pat. No. 5,707,745 to Forrest et al, which isincorporated by reference in its entirety. The OLED structure maydeviate from the simple layered structure illustrated in FIGS. 1 and 2.For example, the substrate may include an angled reflective surface toimprove out-coupling, such as a mesa structure as described in U.S. Pat.No. 6,091,195 to Forrest et al., and/or a pit structure as described inU.S. Pat. No. 5,834,893 to Bulovic et al., which are incorporated byreference in their entireties.

Unless otherwise specified, any of the layers of the various embodimentsmay be deposited by any suitable method. For the organic layers,preferred methods include thermal evaporation, ink-jet, such asdescribed in U.S. Pat. Nos. 6,013,982 and 6,087,196, which areincorporated by reference in their entireties, organic vapor phasedeposition (OVPD), such as described in U.S. Pat. No. 6,337,102 toForrest et al., which is incorporated by reference in its entirety, anddeposition by organic vapor jet printing (OVJP), such as described inU.S. patent application Ser. No. 10/233,470, now U.S. Pat. No.7,431,968, which is incorporated by reference in its entirety. Othersuitable deposition methods include spin coating and other solutionbased processes. Solution based processes are preferably carried out innitrogen or an inert atmosphere. For the other layers, preferred methodsinclude thermal evaporation. Preferred patterning methods includedeposition through a mask, cold welding such as described in U.S. Pat.Nos. 6,294,398 and 6,468,819, which are incorporated by reference intheir entireties, and patterning associated with some of the depositionmethods such as ink jet and OVJD. Other methods may also be used. Thematerials to be deposited may be modified to make them compatible with aparticular deposition method. For example, substituents such as alkyland aryl groups, branched or unbranched, and preferably containing atleast 3 carbons, may be used in small molecules to enhance their abilityto undergo solution processing. Substituents having 20 carbons or moremay be used, and 3-20 carbons is a preferred range. Materials withasymmetric structures may have better solution processibility than thosehaving symmetric structures, because asymmetric materials may have alower tendency to recrystallize. Dendrimer substituents may be used toenhance the ability of small molecules to undergo solution processing.

Devices fabricated in accordance with embodiments of the invention maybe incorporated into a wide variety of consumer products, including flatpanel displays, computer monitors, televisions, billboards, lights forinterior or exterior illumination and/or signaling, heads up displays,fully transparent displays, flexible displays, laser printers,telephones, cell phones, personal digital assistants (PDAs), laptopcomputers, digital cameras, camcorders, viewfinders, micro-displays,vehicles, a large area wall, theater or stadium screen, or a sign.Various control mechanisms may be used to control devices fabricated inaccordance with the present invention, including passive matrix andactive matrix. Many of the devices are intended for use in a temperaturerange comfortable to humans, such as 18° C. to 30° C., and morepreferably at room temperature (20 to 25° C.).

The materials and structures described herein may have applications indevices other than OLEDs. For example, other optoelectronic devices suchas organic solar cells and organic photodetectors may employ thematerials and structures. More generally, organic devices, such asorganic transistors, may employ the materials and structures.

In an embodiment of the present invention, a phosphorescent compoundhaving improved efficiency when incorporated into an OLED is provided.The emissive compound has the following structure (Formula I):

wherein

-   -   M is a metal having an atomic weight greater than 40;    -   (C—N) is a substituted or unsubstituted cyclometallated ligand,        and (C—N) is different from at least one other ligand attached        to the metal;    -   each of R₈ to R₁₄ is independently selected from hydrogen,        alkyl, alkenyl, alkynyl, alkylaryl, CN, CF₃, NO₂, halo, aryl,        heteroaryl, substituted aryl, substituted heteroaryl, or a        heterocyclic group;    -   m may be 0, or have a value of at least 1;    -   n has a value of at least 1, where, when n is 3, none of R₈ to        R₁₄ is a cyano group; and    -   m+n is the maximum number of ligands that may be attached to the        metal; and    -   optionally, any two adjacent substituted positions together        form, independently, a fused 4- to 7-member cyclic group,        wherein said cyclic group is cycloalkyl, cycloheteroalkyl, aryl,        or heteroaryl, and wherein the 4- to 7-member cyclic group may        be optionally substituted with substituent R. Preferably, at        least one of R₈ to R₁₄ is phenyl or substituted phenyl, and/or        at least two of R₈ to R₁₄ that are adjacent are part of a        fluorenyl group.

M may be any metal having an atomic weight greater than 40. Preferredmetals include Ir, Pt, Pd, Rh, Re, Os, Tl, Pb, Bi, In, Sn, Sb, Te, Au,and Ag. More preferably, the metal is Ir or Pt. Most preferably, themetal is Ir.

The term “halo” or “halogen” as used herein includes fluorine, chlorine,bromine, and iodine.

The term “alkyl” as used herein contemplates both straight and branchedchain alkyl radicals. Preferred alkyl groups are those containing fromone to fifteen carbon atoms and includes methyl, ethyl, propyl,isopropyl, butyl, isobutyl, tert-butyl, and the like. Additionally, thealkyl group may be optionally substituted with one or more substituentsselected from halo, CN, CO₂R, C(O)R, NR₂, cyclic-amino, NO₂, and OR.

The term “cycloalkyl” as used herein contemplates cyclic alkyl radicals.Preferred cycloalkyl groups are those containing 3 to 7 carbon atoms,and include cyclopropyl, cyclopentyl, cyclohexyl, and the like.Additionally, the cycloalkyl group may be optionally substituted withone or more substituents selected from halo, CN, CO₂R, C(O)R, NR₂,cyclic-amino, NO₂, and OR.

The term “alkenyl” as used herein contemplates both straight andbranched chain alkene radicals. Preferred alkenyl groups are thosecontaining two to fifteen carbon atoms. Additionally, the alkenyl groupmay be optionally substituted with one or more substituents selectedfrom halo, CN, CO₂R, C(O)R, NR₂, cyclic-amino, NO₂, and OR.

The term “alkynyl” as used herein contemplates both straight andbranched chain alkyne radicals. Preferred alkyl groups are thosecontaining two to fifteen carbon atoms. Additionally, the alkynyl groupmay be optionally substituted with one or more substituents selectedfrom halo, CN, CO₂R, C(O)R, NR₂, cyclic-amino, NO₂, and OR.

The terms “alkylaryl” as used herein contemplates an alkyl group thathas as a substituent an aromatic group. Additionally, the alkylarylgroup may be optionally substituted on the aryl with one or moresubstituents selected from halo, CN, CO₂R, C(O)R, NR₂, cyclic-amino,NO₂, and OR.

The term “heterocyclic group” as used herein contemplates non-aromaticcyclic radicals. Preferred heterocyclic groups are those containing 3 or7 ring atoms which includes at least one hetero atom, and includescyclic amines such as morpholino, piperidino, pyrrolidino, and the like,and cyclic ethers, such as tetrahydrofuran, tetrahydropyran, and thelike.

The term “aryl” or “aromatic group” as used herein contemplatessingle-ring groups and polycyclic ring systems. The polycyclic rings mayhave two or more rings in which two carbons are common by two adjoiningrings (the rings are “fused”) wherein at least one of the rings isaromatic, e.g., the other rings can be cycloalkyls, cycloalkenyls, aryl,heterocycles and/or heteroaryls.

The term “heteroaryl” as used herein contemplates single-ringhetero-aromatic groups that may include from one to three heteroatoms,for example, pyrrole, furan, thiophene, imidazole, oxazole, thiazole,triazole, pyrazole, pyridine, pyrazine, pyrimidine, and the like. Theterm heteroaryl also includes polycyclic hetero-aromatic systems havingtwo or more rings in which two atoms are common to two adjoining rings(the rings are “fused”) wherein at least one of the rings is aheteroaryl, e.g., the other rings can be cycloalkyls, cycloalkenyls,aryl, heterocycles and/or heteroaryls.

All value ranges, for example those given for n and m, are inclusiveover the entire range. Thus, for example, a range between 0-4 wouldinclude the values 0, 1, 2, 3, and 4.

A photoactive ligand is referred to as “photoactive” because it isbelieved that it directly contributes to the photoactive properties ofthe emissive material. Whether a ligand is photoactive depends upon thespecific compound in which the ligand is present. For example, each ofthe ppy ligands of Ir(ppy)₃ is considered photoactive. However, in thecompound (ppy)₂IrX, having two ppy ligands coordinated to the Ir, aswell as an X ligand coordinated to the Ir, the ppy ligands may not bephotoactive, particularly if the X ligand has a lower triplet energythan the ppy ligands. Preferred photoactive ligands include tpy, ppy,4,6-F₂ppy, 4-MeO-4,6-F₂ppy, 4′-DMA-4,6-F₂ppy, 2-ppy, and 2-thpy. Otherexamples of photoactive ligands are disclosed in U.S. patent applicationSer. No. 10/289,915 to Brown et al. (published as Publication No.2004/0096743), which is incorporated by reference in its entirety.

Each of n and m represents the number of ligands of a particular type ina compound. Each of the particular types of ligands may or may not emitat room temperature, depending upon the specific compound in which theligand is present. As used herein, n has a value of at least 1, and mmay be 0, or have a value of at least 1. The maximum number of ligandsthat may be attached to the metal is m+n.

In a preferred embodiment, n is 2.

The compound of the embodiments of the present invention comprises atleast one photoactive ligand of Formula I and a heavy metal ion suchthat the resulting material has (i) a carbon-metal bond and (ii) anitrogen-metal bond. Thus the compounds of the embodiments of thepresent invention comprise a partial structure of

wherein the metal M and each substituent R are defined according to thedefinition of Formula I.

In an embodiment of the invention, the emissive compound comprises aligand having the structure:

wherein each of R₈ to R₁₄ is defined according to the definition ofFormula I.

An embodiment of the invention comprises a compound with the structure

wherein the metal M, each substituent R, m, n, and (C—N) are definedaccording to the definition of Formula I. Preferably, M is iridium. Inanother preferred embodiment, R₈, R₁₀, and R₁₂-R₁₄ are hydrogen. In amost preferred embodiment, n is 2 and m is one. An embodiment of thisinvention includes a ligand with the following structure:

Preferably, each R is hydrogen.

Preferred embodiments of the invention include the following structures:

In another embodiment, the compound of Formula I comprises a structuresuch that n is the maximum number of ligands that may be attached to themetal M, and m is zero. In this embodiment, M and each substituent R,are defined according to the definition of Formula I, with the notableexception that R is not a cyano group. An embodiment of this inventionincludes a compound with the structure

wherein X is independently selected from hydrogen, alkyl, alkenyl,alkynyl, alkylaryl, CN, CF₃, CO₂R, C(O)R, NR₂, NO₂, OR, halo, aryl,heteroaryl, substituted aryl, substituted heteroaryl, or a heterocyclicgroup, and Z is selected from —CH₂, —CRR, —NH, —NR, —O, —S, and —SiR.Preferably, M is iridium and each R is hydrogen. An embodiment of thisinvention includes a ligand with the following structure:

where X, Z, R₈, and R₁₁ to R₁₄ are defined above. Preferably, each R ishydrogen.

Homoleptic (all the ligands attached to the metal center have the samestructure) iridium complexes employing phenylpyrazole derivatives asligands, such as the above embodiment, have been found to be displaypoor electroluminescent qualities. Such complexes are observed not toemit light at room temperature, in either fluid solution or in the solidstate. However, a cyano substituted iridium phenylpyrazole complex haspreviously been reported to emit light at room temperature at a peakwavelength of around 450 nm. Kwon et al., “Blue PhosphorescentCyclometallated Iridium Complex through phenylpyrazole derivatives:Synthesis, Characterization and B3LYP Density functional Theory (DFT)Calculations,” 4th International Conference on Electroluminescence ofMolecular Materials and Related Phenomena, Aug. 27 to 30, 2004, JejuIsland, Korea. Homoleptic iridium complexes are observed to emit in theUV region at 77K at peak wavelength values around 400 nm. It is believedthat employing certain substituents on the phenylpyrazole ligandsignificantly improves luminescent efficiencies. Specifically it isbelieved that substitution of phenyl, napthyl, or pyridyl groups in thephenylpyrazole ligand improves the device lifetime and enhanceselectroluminescent efficiencies. Additionally, it is believed thatfusing the adjacent substituents of the phenylpyrazole ligand alsoimproves the lifetime and efficiency of the device. These substituentsare provided as non-limiting examples, and other substitutedphenylpyrazole ligands exhibiting improved lifetime and enhancedluminescence may be employed.

In a preferred embodiment, one or more of the substituent R, as definedin Formula I, is phenyl, napthyl, or pyridyl, which may be substitutedor unsubstituted. Preferably at least one substituent R is phenyl.Preferred embodiments include compounds having the following structures:

wherein the metal M, each substituent R, m, n, and (C—N) are definedaccording to the definition of Formula I. X is independently selectedfrom hydrogen, alkyl, alkenyl, alkynyl, alkylaryl, CN, CF₃, CO₂R, C(O)R,NR₂, NO₂, OR, halo, aryl, heteroaryl, substituted aryl, substitutedheteroaryl, or a heterocyclic group. Additionally or alternatively, anytwo adjacent substituted positions together form, independently, a fused4- to 7-member cyclic group, which may be cycloalkyl, cycloheteroalkyl,aryl, or heteroaryl, and the 4- to 7-member cyclic group may be furthersubstituted by substituent X. Preferred embodiments of this inventioninclude ligands with the following structure:

wherein each substituent R is defined according to the definition ofFormula I. X is independently selected from hydrogen, alkyl, alkenyl,alkynyl, alkylaryl, CN, CF₃, CO₂R, C(O)R, NR₂, NO₂, OR, halo, aryl,heteroaryl, substituted aryl, substituted heteroaryl, or a heterocyclicgroup. Additionally or alternatively, any two adjacent substitutedpositions together form, independently, a fused 4- to 7-member cyclicgroup, which may be cycloalkyl, cycloheteroalkyl, aryl, or heteroaryl,and the 4- to 7-member cyclic group may be further substituted bysubstituent X.

In another embodiment, at least two substituent R, as defined in FormulaI, are fused to form a 4- to 7-member cyclic group, which may beoptionally substituted. In preferred embodiments, the substituents forma 5- or 6-member cyclic groups. Preferred embodiments include compoundshaving the following structures:

wherein the metal M, each substituent R, m, n, and (C—N) are definedaccording to the definition of Formula I. X is independently selectedfrom hydrogen, alkyl, alkenyl, alkynyl, alkylaryl, CN, CF₃, CO₂R, C(O)R,NR₂, NO₂, OR, halo, aryl, heteroaryl, substituted aryl, substitutedheteroaryl, or a heterocyclic group. Additionally or alternatively, anytwo adjacent substituted positions together form, independently, a fused4- to 7-member cyclic group, which may be cycloalkyl, cycloheteroalkyl,aryl, or heteroaryl, and the 4- to 7-member cyclic group may be furthersubstituted by substituent X. Z is selected from —CH₂, —CRR, —NH, —NR,—O, —S, and —SiR. Preferred embodiments of this invention includeligands with the following structure:

wherein each substituent R is defined according to the definition ofFormula I. X is independently selected from hydrogen, alkyl, alkenyl,alkynyl, alkylaryl, CN, CF₃, CO₂R, C(O)R, NR₂, NO₂, OR, halo, aryl,heteroaryl, substituted aryl, substituted heteroaryl, or a heterocyclicgroup. Additionally or alternatively, any two adjacent substitutedpositions together form, independently, a fused 4- to 7-member cyclicgroup, which may be cycloalkyl, cycloheteroalkyl, aryl, or heteroaryl,and the 4- to 7-member cyclic group may be further substituted bysubstituent X. Z is selected from —CH₂, —CRR, —NH, —NR, —O, —S, and—SiR.

In a preferred embodiment of the present invention, the substitutedphenylpyrazole metal complex is heteroleptic. In a heteroleptic metalcomplex, a ligand attached to the metal center has a different structurefrom at least one other ligand. Preferably, at least one ligand is aphosphorescent emissive ligand at room temperature and at least oneligand is not a phosphorescent emissive ligand at room temperature. Morepreferably, only one ligand is a phosphorescent emitter at roomtemperature. A heteroleptic complex of embodiments of the presentinvention has several advantages over a homoleptic metal complex. It isbelieved that the likelihood of intermolecular quenching is lower forheteroleptic complexes of embodiments of the present invention than forhomoleptic complexes due to lower density of favorable energy transfersites associated with heteroleptic complexes. For example,bis-(1-(4,6-difluoro-phenyl)pyrazolato,N,C^(2′)) iridium(phenylpyridinato,N,C²), which is a specific embodiment of the presentinvention in which there is only one emissive ligand attached to themetal center, the triplet is localized on the emissive ligand (i.e.,phenylpyridinato). A favorable reduction of intermolecular quenchingleads to increased device efficiency.

Moreover, it is believed that substituting fluorine in ligands of theembodiments of the present invention generally increases the tripletenergy of the substituted ligands. Consequently, one method of designingfor a ligand with sufficiently high triplet energy such that the ligandis non-emissive is by substituting fluorine for hydrogens of thephenylpyrazole ligands of the embodiments of the present invention.

In a preferred embodiment, in which the cyclometallated complex isheteroleptic, an emissive ligand has a triplet energy corresponding to awavelength that is at least 80 nm greater than the wavelengthcorresponding to the triplet energy of non-emissive ligands. Theemissive ligand may have a triplet energy corresponding to a wavelengthof 500-520 nm. In another embodiment, the emissive ligand has a tripletenergy corresponding to a wavelength greater than 590 nm. In a preferredembodiment, the emissive ligand has a triplet energy corresponding to awavelength less than 480 nm. In one embodiment, there is only oneemissive ligand at room temperature. Ligands that are emissive incertain compounds may be non-emissive in other compounds due to thepresence of other ligands having lower triplet energy bound to the samemetal. In this case, energy is transferred from the ligand with highertriplet energy to the ligand with lower triplet energy, andconsequently, the ligand initially with the higher triplet energy doesnot contribute to the emission. In another embodiment, there is only oneemissive ligand at room temperature and this ligand is organometallic.

In another embodiment, each ligand coordinated to the metal forms anorganometallic bond with the metal. Organometallic ligands are believedto be more thermally stable than non-organometallic ligands, whencoordinated to third row transition metals, such as Ir and Pt. In apreferred embodiment, in which the cyclometallated complex isheteroleptic, two non-emissive ligands are coordinated to iridium. Inthis case, the luminescent spectrum is observed to be blue-shiftedrelative to the spectrum of a homoleptic organometallic cyclometallatedcomplex of embodiments of the present invention. The blue spectral shiftis believed to result from a strong field interaction between the carbonand metal atoms in an organometallic complex.

For the synthesized complexes of the present invention, it was observedthat the meridional and facial isomers behave similarly. Thus, it isbelieved that the choice of positional isomers does not significantlyaffect device performance. Meridional isomers may be preferred as theyare found to be synthesized more readily. For example, a facial isomeris generally synthesized by converting a meridional isomer. Facialisomers may be preferred, as they are presently the most common isomersin organometallic compounds.

It is understood that the various embodiments described herein are byway of example only, and are not intended to limit the scope of theinvention. For example, many of the materials and structures describedherein may be substituted with other materials and structures withoutdeviating from the spirit of the invention. It is understood thatvarious theories as to why the invention works are not intended to belimiting. For example, theories relating to charge transfer are notintended to be limiting.

Material Definitions

As used herein, abbreviations refer to materials as follows:

-   CBP: 4,4′-N,N-dicarbazole-biphenyl-   m-MTDATA tris(3-methylphenylphenylamino)triphenylamine-   Alq₃: 8-tris-hydroxyquinoline aluminum-   Bphen: 4,7-diphenyl-1,10-phenanthroline-   n-BPhen: n-doped BPhen (doped with lithium)-   F₄-TCNQ: tetrafluoro-tetracyano-quinodimethane-   p-MTDATA: p-doped m-MTDATA (doped with F₄-TCNQ)-   Ir(ppy)₃: tris(2-phenylpyridine)-iridium-   Ir(ppz)₃: tris(1-phenylpyrazoloto,N,C(2′)iridium(III)-   BCP: 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline-   TAZ: 3-phenyl-4-(1′-naphthyl)-5-phenyl-1,2,4-triazole-   CuPc: copper phthalocyanine-   ITO: indium tin oxide-   NPD: N,N′-diphenyl-N—N′-di(1-naphthyl)-benzidine-   TPD: N,N′-diphenyl-N—N′-di(3-toly)-benzidine-   BAlq:    aluminum(III)bis(2-methyl-8-hydroxyquinolinato)4-phenylphenolate-   mCP: 1,3-N,N-dicarbazole-benzene-   DCM: 4-(dicyanoethylene)-6-(4-dimethylaminostyryl-2-methyl)-4H-pyran-   DMQA: N,N′-dimethylquinacridone-   PEDOT:PSS: an aqueous dispersion of poly(3,4-ethylenedioxythiophene)    with polystyrenesulfonate (PSS)-   tpy: 2-(p-tolyl)pyridine-   ppy: 2-phenylpyridine-   4,6-F₂ppy: 2-(4′,6′-difluorophenyl)pyridine-   4-MeO-4,6-F₂ppy: 2-(4′,6′-difluorophenyl)-4-methoxypyridine-   4′-DMA-4,6-F₂ppy:    2-(4′,6′-difluorophenyl)-4-(N,N-dimethylamino)pyridine-   2-thpy: 2-(2′-thienyl)pyridine-   (46dfppz)₂Ir(ppy): bis(1-(4,6-difluorophenyl)pyrazolato-N,C^(2′))    Iridium(III) (2-phenylpyridinato-N,C^(2′))-   (46dfppz)₂Ir(tpy): bis(1-(4,6-difluorophenyl)pyrazolato-N,C^(2′))    Iridium(III) (2-(p-tolyl)pyridinato-N,C^(2′))-   (46dfppz)₂Ir(4′,6′-F₂ppy):    bis(1-(4,6-difluorophenyl)pyrazolato-N,C^(2′)) Iridium(III)    (2-(4′,6′-difluorophenyl)pyridinato-N,C^(2′))-   (46dfppz)₂Ir(4-MeO-4′,6′-F₂ppy):    bis(1-(4,6-difluorophenyl)pyrazolato-N,C^(2′)) Iridium(III)    (2-(4′,6′-difluorophenyl)-4-methoxypyridinato-N,C^(2′))-   (46dfppz)₂Ir(4-DMA-4′,6′-F₂ppy):    bis(1-(4,6-difluorophenyl)pyrazolato-N,C^(2′)) Iridium(III)    (2-(4′,6′-difluorophenyl)-4-(N,N′-dimethylamino)pyrid    inato-N,C^(2′))-   3bppz: 1-(3-biphenyl)pyrazole-   4bppz: 1-(4-biphenyl)pyrazole-   14dppz: 1,4-diphenylpyrazole-   4bpppz: 1-(4-biphenyl)-4-phenylpyrazole-   2dmflpz: 1-(2-(9,9-dimethyl)fluorenyl)pyrazole-   3dmflpz: 1-(3-(9,9-dimethyl)fluorenyl)pyrazole-   fac-Ir(3bppz)₃:    fac-tris(1-(3-biphenyl)pyrazolato-N,C^(2′))iridium(III)-   fac-Ir(4bppz)₃:    fac-tris(1-(4-biphenyl)pyrazolato-N,C^(2′))iridium(III)-   fac-Ir(14dppz)₃:    fac-tris(1,4-diphenylpyrazolato-N,C^(2′))iridium(III)-   fac-Ir(4bpppz)₃:    fac-tris(1-(4-biphenyl)-4-phenylpyrazolato-N,C^(2′))iridium(III)-   fac-Ir(2dmflpz)₃:    fac-tris(1-(2-(9,9dimethyl)fluorenyl)pyrazolato-N,C^(2′))iridium(III)

Experimental

Specific representative embodiments of the invention will now bedescribed, including how such embodiments may be made. It is understoodthat the specific methods, materials, conditions, process parameters,apparatus, and the like do not necessarily limit the scope of theinvention.

EXAMPLE 1 General Synthetic Scheme for a Substituted Phenylpyrazole

Ligands synthesized through the above synthetic route are summarized inTable I.

TABLE I Compound Phenylpyrazole ligand (46dfppz)₂Ir(ppy)(46dfppz)₂Ir(tpy) (46dfppz)₂Ir(4′,6′-F₂ppy)(46dfppz)₂Ir(4-MeO-4′,6′-F₂ppy) (46dfppz)₂Ir(4′-DMA-4′,6′-F₂ppy)

fac-Ir(14dppz)₃

EXAMPLE 2 General Synthetic Scheme for a Biphenylpyrazole

Ligands synthesized through the above synthetic route are summarized inTable II.

TABLE II Compound Phenylpyrazole ligand fac-Ir(3bppz)₃

fac-Ir(4bppz)₃

fac-Ir(4bpppz)₃

EXAMPLE 3 Synthesis of 2dmflpz Ligand

EXAMPLE 4 Synthesis of 3dmflpz Ligand

EXAMPLE 5 Synthesis of Meridional Isomers of (46dfppz)₂Ir(ppy),(46dfppz)₂Ir(tpy), (46dfppz)₂Ir(4′,6′-F₂ppy),(46dfppz)₂Ir(4-MeO-4′,6′-F₂ppy), and (46dfppz)₂Ir(4′-DMA-4′,6′-F₂ppy)

[(46dfppz)₂IrCl]₂ complex, 1-1.05 equivalent of the appropriate ligand,5-10 equivalent of K₂CO₃ were heated to 140-145° C. under inertatmosphere in glycerol for 20-24 hours. After the mixture was cooled toroom temperature, distilled water was added, and the resultingprecipitate was filtered off, washed with several portions of distilledwater, and air-dried. The crude product was then flashed chromatographedon a silica column using dichloromethane to provide 60-80% of puremeridional heteroleptic iridium tris-cyclometallated complex.

EXAMPLE 6 Synthesis of Facial Isomers of (46dfppz)₂Ir(ppy),(46dfppz)₂Ir(tpy), (46dfppz)₂Ir(4′,6′-F₂ppy),(46dfppz)₂Ir(4-MeO-4′,6′-F₂ppy), and (46dfppz)₂Ir(4-DMA-4′,6′-F₂ppy)

An argon-degassed solution of the meridional complex in acetonitrile wasirradiated with UV light (254 nm or 360 nm) for 24-48 hours, after whichthe solvent was removed in vacuo. The crude product was thenchromatographed on a silica column using dichloromethane to provide >90%of pure facial heteroleptic iridium tris-cyclometallated complex.

EXAMPLE 7 Synthesis of fac-Ir(3bppz)₃, fac-Ir(4bppz)₃, fac-Ir(14dppz)₃,fac-Ir(4bpppz)₃, fac-Ir(2dmflpz)₃, and Ir(ppz)₃

[(C^N)₂Ir(O^O)] complex, 1-1.1 equivalent of the appropriatecyclometallating ligand, were refluxed under inert gas atmosphere inglycerol for 20-24 hours. After the mixture was cooled to roomtemperature, distilled water was added, and the resulting precipitatewas filtered off, washed with several portions of distilled water, andair-dried. The crude product was then flashed chromatographed on asilica column using dichloromethane to provide 60-80% of pure facialheteroleptic iridium tris-cyclometallated complex.

Table III summarizes the photophysical properties of compounds ofExamples 5 and 6.

TABLE III CIE coordi- Room nates Temp 77 K (PL in Emission EmissionCompound Structure solution) (nm) (nm) (46dfppz)₂Ir(ppy)

0.14, 0.43 476 466, 502 (46dfppz)₂Ir(tpy)

0.15, 0.41 476 466, 502 (46dfppz)₂Ir(4′,6′- F₂ppy)

0.14, 0.27 462, 488 448, 480 (46dfppz)₂Ir(4-MeO- 4′,6′-F₂ppy)

0.14, 0.19 454, 478 460, 440, 432 (46dfppz)₂Ir(4′- DMA-4′,6′-F₂ppy).

0.15, 0.13 446, 466 430, 456

Table IV summarizes the electrochemical and photophysical properties ofthe fac-Ir(C—N)₃ complexes. The oxidation and reduction potentials weremeasured in anhydrous DMF using ferrocene as reference. All reductionpotentials are irreversible. The spectral and lifetime data wereobtained using 2-Me THF solutions that were bubble degassed with N₂.

TABLE IV Room Room Temp. 77 K 77 K Temp. Lifetime λ_(max) LifetimeComplex E_(oxidation) E_(reduction) λ_(max) (nm) (μs) (nm) (μs)Comparative 0.390 — — — 414 14 Irppz fac-Ir(3bppz)₃ 0.427 −2.916 466 —460 26.9 fac-Ir(4bppz)₃ 0.644 −3.048 420 — 414 20.8 fac-Ir(14dppz)₃0.393 −3.060 426 — 422 5.7; 13.6 fac-Ir(4bpppz)₃ 0.424 −2.879 478 2.6472 32.6 fac-Ir(2dmflpz)₃ 0.321 −3.049 478 1.7 476 28.8

FIG. 3 shows the emission spectra at 77 K for fac-Ir(3bppz)₃,fac-Ir(4bppz)₃, fac-Ir(14dppz)₃, fac-Ir(4bpppz)₃, fac-Ir(2dmflpz)₃.

FIG. 4 shows the emission spectra at room temperature forfac-Ir(3bppz)₃, fac-Ir(4bppz)₃, fac-Ir(14dppz)₃, fac-Ir(4bpppz)₃,fac-Ir(2dmflpz)₃.

FIG. 5 shows the emission spectra for fac-Ir(14dppz)₃, fac-Ir(4bpppz)₃,fac-Ir(2dmflpz)₃ in polystyrene at room temperature.

While the present invention is described with respect to particularexamples and preferred embodiments, it is understood that the presentinvention is not limited to these examples and embodiments. The presentinvention as claimed therefore includes variations from the particularexamples and preferred embodiments described herein, as will be apparentto one of skill in the art.

1. A compound, having the structure:

wherein M is a metal having an atomic weight greater than 40; (C—N) is asubstituted or unsubstituted cyclometallated ligand; wherein at leastone ligand functions as a phosphorescent emissive ligand in the compoundat room temperature and at least one ligand does not function as aphosphorescent emissive ligand in the compound at room temperature;wherein the emissive ligand in the compound at room temperature has atriplet energy corresponding to a wavelength that is at least 80 nmgreater than the wavelength corresponding to the triplet energy of aligand that is not emissive in the compound at room temperature; each ofR₈ and R₁₁ to R₁₄ is independently selected from hydrogen, alkyl,alkenyl, alkynyl, alkylaryl, CF₃, NO₂, halo, aryl, heteroaryl,substituted aryl, substituted heteroaryl, or a heterocyclic group; Z isselected from —CH₂—, substituted carbon, NH, substituted nitrogen, —O—,—S—, and substituted silicon; optionally, any two adjacent substitutedpositions together form, independently, a fused 4- to 7-member cyclicgroup, wherein said cyclic group is cycloalkyl, cycloheteroalkyl, aryl,or heteroaryl, and wherein the 4- to 7-member cyclic group may beoptionally substituted; X is independently selected from hydrogen,alkyl, alkenyl, alkynyl, alkylaryl, CN, CF₃, NO₂, halo, aryl,heteroaryl, substituted aryl, substituted heteroaryl, or a heterocyclicgroup; n has a value of at least 1; and m+n is the maximum number ofligands that may be attached to the metal.
 2. The compound of claim 1,wherein M is selected from the group consisting of Ir, Pt, Pd, Rh, Re,Ru, Os, Tl, Pb, Bi, In, Sn, Sb, Te, Au, and Ag.
 3. The compound of claim2, wherein M is Ir.
 4. The compound of claim 3, wherein R₈, and R₁₁-R₁₄are H.
 5. The compound of claim 1, wherein the emissive ligand has atriplet energy corresponding to a wavelength of 500-520 nm.
 6. Thecompound of claim 1, wherein the emissive ligand has a triplet energycorresponding to a wavelength greater than 590 nm.
 7. An organic lightemitting device, comprising: an anode; a cathode; and an emissive layerdisposed between the anode and the cathode, the emissive layercomprising a compound of claim
 1. 8. The device of claim 7, wherein M isselected from the group consisting of Ir, Pt, Pd, Rh, Re, Ru, Os, Tl,Pb, Bi, In, Sn, Sb, Te, Au, and Ag.
 9. The device of claim 8, wherein Mis Ir.
 10. The device of claim 9, wherein R₈, and R₁₁-R₁₄ are H.
 11. Thedevice of claim 7, wherein the emissive ligand has a triplet energycorresponding to a wavelength of 500-520 nm.
 12. The device of claim 7,wherein the emissive ligand has a triplet energy corresponding to awavelength greater than 590 nm.
 13. The device of claim 7, wherein the“n”-bracketed ligand functions as a phosphorescent emissive ligand inthe compound.
 14. The device of claim 7, wherein Z is selected from—CH₂— or substituted carbon.
 15. The device of claim 14, wherein M isiridium.
 16. The device of claim 15, wherein R₈ and R₁₁-R₁₄ are H. 17.The device of claim 7, wherein the “n”-bracketed ligand in the compoundis 1-(2-(9,9-dimethyl)fluorenyl)pyrazole.
 18. The device of claim 7,wherein the compound is a blue-emitting phosphorescent emissivematerial.